CHRYSLER PT CRUISER STEERING PROBLEM

2002 Chrysler PT Cruiser

Hello, I have a Chrysler 2002 PT Cruiser Classic. When turned into my daughter's school the wheel tightened and it made a very loud squeaking noise. My husband checked the steering fluid and it was low. We purchased more and he filled it up. On our way home when we made slight turns to the left or right, the steering wheel felt better and was more loose, but the second I made more of a sharp turn into our parking lot the steering wheel tightened again and the loud squeak was present. Could this possibly mean we need a new power steering unit? Appreciate any advice you could give us, Thanks!